1. Field of the Invention
The present invention relates to a height adjustment device, and more specifically, to a height adjustment device with fine-tuning for an image system.
2. Description of the Prior Art
Image systems like projectors at the present time are usually either configured on the ceiling to cast images onto a project screen in a nearly horizontal way or on a desk and cast images in an elevation angle. Except for the first way to fix the projectors on the ceiling, which is generally used in a large meeting room environment, as the portability of presentation systems or movie playback systems is concerned, most projectors with high mobility adopt the second way, i.e., to place the projector on a surface (generally on a desk lower than the project screen) and by providing the adjustability of the projection lens' height and of the built-in trapezoid distortion parameter of the projectors, the images can be cast on a wall or the project screen.
The conventional height adjustment devices of a projector can be categorized in two. A first type has rack with fixed teeth distance and to adjust the height of the adjustment device, simply press an actuator that engages with the rack to release the rack so that the adjustment device can be adjusted to a needed height. Afterward, the actuator engages with the rack again to keep the adjustment device at the needed height. The first type of the height adjustment devices provides fast adjustment for configuring the projector but the precision for adjusting the height is also limited by the fixed distance of the rack and is rather rough due to manufacture limitation of the rack.
A second type of conventional height adjustment devices utilizes screw for height adjusting, which has very high precision. However, this type of height adjustment devices is too poor in efficiency for adjustment compared to the previous first type height adjustment devices since rotating the screw every single round only moves the height adjustment device a tooth distance of the screw in height.
An improved height adjustment device combining the features of both previous two types utilizes a latch to engage with the screw. The screw can move in a large scale with the latch disengaged and also rotate in a fine scale with the latch engaged. Such type of height adjustment device is also disclosed in the Taiwan patent #528,916. Even so, it always requires two separate operations to satisfy the requirement of precision and efficiency for the height adjustment devices in image systems such as the projectors. Situations below happen quite frequently: users know how to operate one operation (adjusting in a large scale or fine-tuning) while the other operation is always forgotten.